The chemoreflex: adult versus child comparison.

Purpose: Compare the influence of the chemoreflex on heart rate (HR) and blood pressure (BP) responses between children and adults.

Methods: Seventy children (35 boys and 35 girls) and 70 adults (35 men and 35 women) performed 30% maximal voluntary contraction static handgrip exercise (SHG) for 3 min, followed by 4 min of muscle ischemia and then 6 min of recovery, while HR and BP were measured.

Results: During 3 min of SHG, systolic BP (SBP) increased significantly more in men versus boys (23+/-9 vs 18+/-9%) and women versus girls (21+/-10 vs 15+/-7%), respectively. Diastolic BP (DBP) increased similarly during SHG in adults versus children. During SHG, HR increased similarly in males but significantly more in girls versus women (16+/-10 vs 11+/-9%), respectively. During occlusion, HR fell to baseline and remained through recovery in adults and children. Both SBP and DBP decreased similarly during the first minute of occlusion but remained significantly above baseline in adults and children. During the first minute of recovery, BP decreased to baseline in adults. In children, DBP decreased but remained significantly above baseline through recovery. SBP decreased in children during minute 1 of recovery yet remained significantly above baseline for 1-2 min in children.

Conclusions: The muscle chemoreflex influence on HR and BP is similar in children and adults as evident in the return of HR to baseline, with a similar concomitant maintenance of BP above baseline during occlusion. When occlusion is released, BP returns to baseline in adults, whereas in children DBP remains significantly above baseline through recovery and SBP for 1-2 min. The differing BP response may be explained by a more active arterial chemoreflex in children.